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VGA to TV not working?

Discussion in 'Video Scalers & Video Processing' started by corsa, Jun 20, 2009.

  1. corsa

    corsa Member

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  2. Liam @ Prog AV

    Liam @ Prog AV Active Member Assured Advertiser

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    This won't work. The only thing you can do is if your laptop has a video output such as s-video or composite video. You can buy boxes to take VGA signal and actively process them down to a video signal, but the results are ropey and the boxes can get very expensive.
  3. Simon Kemp

    Simon Kemp Member

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    So why sell a "VGA to 3 RCA" lead anyway? Is it actually VGA to "Component Video" or VGA to "Composite Video"?
    If it won't do the job it's meant to do then it's not fit for purpose and the buyer should be able to claim a refund!
    And how come a "fuzzy" picture results on the TV set when one wouldn't expect to get any kind of picture at all?
    This has got me totally confused.
  4. Liam @ Prog AV

    Liam @ Prog AV Active Member Assured Advertiser

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    There are many devices which do use those two physical connectors to send usually a component video signal e.g. video processors, plasma displays which accept component video via the VGA socket, some older DVD players used to use VGA type sockets, HDMI-YUV converters.

    You are buying a cable, the cable is fit for it's purpose i.e. connecting a 15 pin sub-d connector to 3 RCA phono connectors. It is the buyers responsibility to know if his kit specifically is capable of receiving/sending the colourspace, resolution and refresh rate needed for it to work. In this case the laptop is not capable of sending component video colourspace. What it is sending is RGBHV colourspace. The TV is picking up the red, green, blue portion of the signal, but it is not receiving the sync signal to generate the image. It is also looking at a different colourspace of component video and so would not be colour accurate. The cable is not being sold as a converter in any way, but what is needed is a conversion from RGBHV to YUV and the laptop to be able to send whatever resolution (if any) the TV is capable of accepting. Otherwise the OP needs to look at alternatives such as s-video connection if the laptop has one.
  5. Simon Kemp

    Simon Kemp Member

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    Dear Liam,
    The HP 6735s laptop computer - like so many nowadays - apparently lacks an S-Video or Composite Video Out port for analogue video. It also lacks either DVI out or HDMI out. I looked up the specifications last night just to check this out! So presumably an RGBHV to YPbPr converter is about the only option for connecting to an HD-ready television set.
    Your explanation about the VGA to 3RCA adapter lead was succinct, concise and helpful. I still can't understand how anyone could get a viewable picture out of the device because it lacks the two extra RCA leads to carry the Horizontal and Vertical synchronisation pulses. Surely any A/V device needs this information to produce a picture? I've tried various permutations of connecting RGB leads into YPbPr sockets, and vice versa, on my own equipment at home and all I ever get is a black TV screen - not even a fuzzy picture.
    I once tried to make myself a VGA to SCART adapter using discarded cables and plugs. Given that the two types of video signal are very similar, could this be a way forward for anyone needing to connect a computer to a TV set? The picture quality from the RGB video input should be almost up to HD standard.
    Thanks again for your prompt and informative response.
    Best regards.
    Yours sincerely,
    Simon Kemp
    S. KEMP
  6. choddo2006

    choddo2006 Member

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    Typically you'd use a 3RCA - VGA to connect a YPbPr output to a d-sub input on a screen which allowed it. So the sync would be vert only and embedded in the Y signal.

    There might be sources out there which can send a component signal out of a d-sub in which case the cable would work as the ebay ad suggests but it's pretty clear they're over-stating its usefulness.

    I guess the assumption is that for £3.45, noone could be arsed to complain.

    p.s. what's with the strange formal letter style in the previous post?
  7. bxd

    bxd Member

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    Hi,

    VGA and scart aren't very similar at all. VGA signals are progressive (rgbhv) while scart (rgb+composite sync) are interlaced.

    A vga to scart cable adapter will only work if the source device can output an interlaced (rgb) signal (possible but unlikely) or if the display can accept a progressive (rgbhv) signal on it's scart input (again unlikely).

    I had an old crt projector (Sony 1031) which would do this and it would happily accept a 480p (vga) or 600p (s-vga) source via it's scart input. I still have the vga to scart adapter lead so it works perfectly well with the right equipment.

    Brian
  8. Liam @ Prog AV

    Liam @ Prog AV Active Member Assured Advertiser

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    I agree Simon I haven't a clue how it picked up a picture at all. I can only assume the TV is picking up some mess from somewhere it is trying to sync with giving a flash of something for just a second. Perhaps cross-talk from one of the sync pins in the d-sub connector on the laptop, I don't really know. Bizarre really.

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